| Fuel cells are considered as one of the most promising technology. Ion exchange membranes(IEM) are the key component of ion exchange membrane fuel cells(IEMFC), which take charge of the performance of IEMFCs, like output power, open-circuit voltage and so forth. This study centers on a key scientific issue-- the structure-activity relationship between ion conduction properties in membranes and the microstructure, chemical structure of membranes. By modeling and analyzing, a guideline is formulated that in order to intensify the proton conduction property in membranes, efforts should be made in the following three aspects: ion mobility, ion density and channel function. Based on this guideline, three relevant methods were come up, in hope of offering some guidance to the R&D of IEM. The details were summarized as follows:1. Intensification of proton conduction property by enhancing ion mobility. Phytic acid and MIL101 were respectively employed as phosphate groups donor and supporters to prepare composite material, which exhibited a low leakage rate of phytic acid and high loading(11.54 wt %). The composite material was incorporated into Nafion to fabricate hybrid membrane, and the hybrid membrane was endowed with excellent ion conductivity at 10.5 % relative humidity(RH), which was 11 times higher than Nafion. The increased ion conductivity is attributed to the following reasons. The degradation of ion conductivity is ascribed to the degradation of ion mobility caused by breakage of hydrogen networks at low humidity. The introduction of phosphate groups into membranes can facilitate the proton transfers via Grotthuss mechanism effectively because that it can construct hydrogen networks by self-dissociation to protect the ion mobility from degradation at low humidity, leading to intensification of proton conduction property.2. Intensification of proton conduction property by enhancing ion density. Ion conductivity always shows a positive relationship with ion density. Thus, increasing the ion density is an easy and effective method to intensify proton conduction property. Imidazolium-functionalized poly(ether ether ketone) with a high functionalization degree was employed as polymer matrix to pursue high ion-exchange capacity of 3.15-2.31 mmol/g-1 as well as high ion density of 1.89-1.80 mmol cm-3, which endow the membranes with high ion conductivity up to 76.38 mS cm-1(80 oC, 100 % RH). In addition, sulfonated poly(ether ether ketone) was employed as ion crosslinking reagent to ensure the stabilities of membranes.Benefiting from the strong electrostatic interaction introduced by the acid-base blending, the stabilities and methanol resistance of blend membranes are enhanced.3. Intensification of proton conduction property by optimizing channel function. Ions cross the membranes through channels. Thus, the properties of channels, like the length of ion pathways, resistance of channels and so forth, are key factors taking charge of the proton conduction property. Crystal MIL101 with cage structure was employed as matrix, and imidazolium was impregnated into MIL101 for endowing it with electroconductibility. The imidazolium-impregnated MIL101 was pressed into inorganic membrane. Drawing support from the highly order lattice of MIL101, ionic highway with shorter length and lower resistance is constructed, endowing the inorganic membrane with high channel function value(73 % higher than Nafion) as well as high ion conductivity of 0.126 mS cm-1(80 oC, 100 % RH). |
